ns4.corpnet.pl has no MX records.
Question and response
Question
dig ns4.corpnet.pl. MX
Answer
The response has no answer records.
Authority
corpnet.pl. 1800 SOA ns1.corpnet.pl. dns-pl.orange.com. 2026021002 10800 3600 604800 1800
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0